Nine flamingos were found headless at the zoo on Friday morning and another six on Saturday.
Police said some of the birds had stab wounds and appealed for witnesses, believing the deaths to be the work of a human.
But on Tuesday, after the dead birds had been examined by a vet, authorities said the deaths were the work of a fox.
Director of the zoo Manfred Niekisch said: "Despite all the sadness and grief over the loss of the animals, we are relieved that we are not dealing with an animal abuser."
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